Deviations from the Isobaric Multiplet Mass Equation due to threshold states

TL;DR

This paper investigates deviations from the Isobaric Multiplet Mass Equation in A=16 nuclei, attributing them to continuum coupling effects near proton decay thresholds, and uses the Shell Model Embedded in the Continuum to explain these isospin violations.

Contribution

It demonstrates that threshold states near decay thresholds exhibit isospin violations explained by continuum coupling effects, advancing understanding of nuclear structure in proton-rich nuclei.

Findings

Deviations are most pronounced for 2+ states.

Continuum coupling explains isospin violations.

Threshold states show energy-dependent continuum effects.

Abstract

Recent studies have completed the A=16 isospin quintets for states with spin/parity J{\pi} =0+ and 2+. The dependence of their masses as a function of isospin projection shows evidence for deviations from quadratic behavior indicating isospin violation beyond the expectation from two- body forces. The deviation is most pronounced for the 2+ states. Predictions from the Shell Model Embedded in the Continuum (SMEC) allow us to explain that this isospin violation is associated with a modification of the nuclear structure due to the open-quantum-system nature of the proton- rich members of the quintet. In particular, the 0+ and 2+ states in 16Ne and the 2+ state in 16F are threshold resonances located just above a proton-decay threshold where s-wave coupling to the continuum is expected. The measured deviations of these threshold states from the quadratic behavior of the remaining members of the multiplets makes it possible to obtain information on the magnitude and the energy dependence of the continuum-coupling energy correction. Continuum coupling is also indicated for the ground state of 8C, but this time through p-wave coupling.